This invention relates to a hoisting winch mounted on a crane or the like, and more particularly to a winch device assembled in the final reduction drive for a spooling drum on a winch and in which when a load which has been hoisted thereby is lowered, free rotation (or idle run) of the spooling drum is controlled by the frictional braking force adjusted by the operator to the degree he desires.
In the past, as disclosed in the U.S. Pat. No. 3,519,247, there has been known a winch device comprising a plurality of spring-applied and hydraulically released frictional disk brakes which, when actuated, arrest rotation of a ring gear and a planetary gear system having a carrier or spider located so as to mesh with the ring gear and connected with a spooling drum of the winch.
According to the winch disclosed in the U.S. Pat. No. 3,519,247, the hoisted load can be lowered by releasing the braking force which holds the ring gear against rotation. Stating in brief, even when the planetary gear system is being rotated by the power transmitted by a prime mover in the same direction as that for hoisting, the spooling drum is permitted to rotate by the weight of the load carried by the crane in the opposite direction to that for hoisting, provided that the braking force applied on the ring gear is released. The carrier connected with the spooling drum is also rotated in the same direction as that of rotation of the spooling drum. When the arresting force on the ring gear is released, the ring gear itself is rotated by the rotation of the planet gear. Accordingly, the rotation of the ring gear will counteract the rotation of the carrier in the direction for hoisting which occurs when the ring gear is arrested, and therefore the spooling drum is allowed to rotate freely by the load carried by the crane in the opposite direction to that for hoisting. Further, in order to control the free rotation of the spooling drum, a metering hydraulic pump is provided which meshes directly with the ring gear and the pressurized fluid delivered by which is utilized to adjust the braking force which arrests rotation of the ring gear.
In the winch device cited above, there is disclosed control by means of the metering pump as means for adjusting the frictional braking force of the disk brake in proportion to the speed of rotation of the ring gear. However, since this metering pump is mounted on the peripheral surface of the casing so as to project out in the radial direction, the structure of the device is not compact. Further it is troublesome to position the pump because of the need for directly engaging a drive pinion of the pump with the ring gear. In addition, in this prior art device, it is difficult to perform a fine control operation, because a control circuit thereof including the metering pump is too simple. Particularly, in this winch device, there is no difficulty encountered in case of simple operations such as hoisting the load and lowering the same by means of a single crane. However, when fine and complicated operations are required as in the case of hoisting and lowering a load by means of two sets of cranes used in such a manner as to cooperate with each other, it has been difficult to adjust quickly the frictional braking force to the degree that the operator desires.